Where can I find crossword puzzles with a specific theme, e.g. history, geography, etc. that are at a level suitable for an adult? I realize that something like history is a very general category, but even if the clues are a hodge-podge, that's fine with me.

I've used search engines to look for puzzles like this, but almost everything I can find is either designed for a classroom and thus geared towards children, or user-generated and far too simple. (This is one absolutely atrocious example).

In response to the comments, I'm interested in puzzles for myself. The topics I listed above, like history and geography, are some of the themes I'm interested in; once again, I realize these are quite general categories.

$\begingroup$What is the purpose of your search? Do you want to get challenges for yourself or do you want to use them elsewhere for others? I'm asking, because if the latter than help on creating such puzzle might be a helpful answer, but obviously not in the first case... And out of curiosity: Why a specific theme - and which one?$\endgroup$
– BmyGuestJun 24 '15 at 21:38